add doc

README.md

@@ -231,7 +231,7 @@ See [examples](examples).
 - [voxel/vx_difference](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_difference.html)
 
 ### Matrix
-- matrix/m_determinant	
+- [matrix/m_determinant](https://openhome.cc/eGossip/OpenSCAD/lib2x-m_determinant.html)
 
 ### Voronoi
 - voronoi/vrn2_from

docs/lib2x-m_determinant.md

@@ -0,0 +1,37 @@
+# m_determinant
+
+It can calculate a determinant, a special number that can be calculated from a square matrix.
+
+**Since:** 2.4
+
+## Parameters
+
+- `m` : A square matrix.
+
+## Examples
+
+    use <matrix/m_determinant.scad>;
+
+    assert(
+        m_determinant([
+            [3, 8],
+            [4, 6]
+        ]) == -14
+    );
+
+    assert(
+        m_determinant([
+            [6,  1, 1],
+            [4, -2, 5],
+            [2,  8, 7]
+        ]) == -306
+    );
+
+    assert(
+        m_determinant([
+            [0,  4, 0, -3],
+            [1,  1, 5,  2],
+            [1, -2, 0,  6],
+            [3,  0, 0,  1]
+        ]) == -250
+    );

src/matrix/m_determinant.scad

@@ -1,3 +1,13 @@
+/**
+* m_determinant.scad
+*
+* @copyright Justin Lin, 2019
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-m_determinant.html
+*
+**/
+
 use <_impl/_m_determinant_impl.scad>;
 
-function m_determinant(matrix) = _m_determinant(matrix);
+function m_determinant(m) = _m_determinant(m);